网站建设规划书,网页视频下载器破解版,wordpress判断浏览器,网站建好后Mybatis中的设计模式 Mybatis中使用了大量的设计模式。 以下列举一些看源码时#xff0c;觉得还不错的用法#xff1a; 创建型模式 工厂方法模式 DataSourceFactory 通过不同的子类工厂#xff0c;实例化不同的DataSource TransactionFactory 通过不同的工厂#xff…Mybatis中的设计模式 Mybatis中使用了大量的设计模式。 以下列举一些看源码时觉得还不错的用法 创建型模式 工厂方法模式 DataSourceFactory 通过不同的子类工厂实例化不同的DataSource TransactionFactory 通过不同的工厂生产不同的Transaction 单例模式 ErrorContext是单例模式但只是线程级别的 private static final ThreadLocalErrorContext LOCAL new ThreadLocal();private ErrorContext() {}public static ErrorContext instance() {ErrorContext context LOCAL.get();if (context null) {context new ErrorContext();LOCAL.set(context);}return context;}Configuration 类虽然正常情况下只有一个实例但是它的设计并不符合单例模式 public Configuration(Environment environment) {this();this.environment environment;}可以看到它的构造器并没有私有化我们可以new多个实例 LogFactory也不是单例模式每次都会通过构造器实例化对象 private LogFactory() {// disable construction}public static Log getLog(Class? aClass) {return getLog(aClass.getName());}public static Log getLog(String logger) {try {return logConstructor.newInstance(logger);} catch (Throwable t) {throw new LogException(Error creating logger for logger logger . Cause: t, t);}}结构型模式 代理模式 在初始化配置时会调用MapperRegistry的addMapper方法将Mapper接口存储在knownMappers中key为Mapper接口value为MapperProxyFactory实例 public T void addMapper(ClassT type) {if (type.isInterface()) {if (hasMapper(type)) {throw new BindingException(Type type is already known to the MapperRegistry.);}boolean loadCompleted false;try {knownMappers.put(type, new MapperProxyFactory(type));// Its important that the type is added before the parser is run// otherwise the binding may automatically be attempted by the// mapper parser. If the type is already known, it wont try.MapperAnnotationBuilder parser new MapperAnnotationBuilder(config, type);parser.parse();loadCompleted true;} finally {if (!loadCompleted) {knownMappers.remove(type);}}}}当我们通过UserMapper mapper sqlSession.getMapper(UserMapper.class);获取Mapper接口时则会调用MapperRegistry#getMapper返回Mapper接口的代理类 public T T getMapper(ClassT type, SqlSession sqlSession) {final MapperProxyFactoryT mapperProxyFactory (MapperProxyFactoryT) knownMappers.get(type);if (mapperProxyFactory null) {throw new BindingException(Type type is not known to the MapperRegistry.);}try {return mapperProxyFactory.newInstance(sqlSession);} catch (Exception e) {throw new BindingException(Error getting mapper instance. Cause: e, e);}}代理类的生成 public T newInstance(SqlSession sqlSession) {final MapperProxyT mapperProxy new MapperProxy(sqlSession, mapperInterface, methodCache);return newInstance(mapperProxy);}protected T newInstance(MapperProxyT mapperProxy) {return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);}可以看到使用的是JDK动态代理MapperProxy实现了InvocationHandler接口我们关注MapperProxy#invoke即可 Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else if (method.isDefault()) {return invokeDefaultMethod(proxy, method, args);}} catch (Throwable t) {throw ExceptionUtil.unwrapThrowable(t);}final MapperMethod mapperMethod cachedMapperMethod(method);return mapperMethod.execute(sqlSession, args);}调用mapper接口最终执行的就是我们编写的SQL 行为型模式 模板方法模式 BaseExecutor BaseExecutor实现了Executor接口定义了模板方法并将钩子方法留给子类实现 模板方法钩子方法querydoQueryupdatedoUpdateflushStatementsdoFlushStatementsqueryCursordoQueryCursor BaseTypeHandler BaseTypeHandler实现了TypeHandler接口定义模板方法将钩子方法留给子类实现 setNonNullParameter getNullableResult 模板方法钩子方法setParametersetNonNullParametergetResult(ResultSet rs, String columnName)getNullableResult(ResultSet rs, String columnName)getResult(ResultSet rs, int columnIndex)getNullableResult(ResultSet rs, int columnIndex)getResult(CallableStatement cs, int columnIndex)getNullableResult(CallableStatement cs, int columnIndex) 策略模式 在DefaultParameterHandler#setParameters中 Overridepublic void setParameters(PreparedStatement ps) {ErrorContext.instance().activity(setting parameters).object(mappedStatement.getParameterMap().getId());ListParameterMapping parameterMappings boundSql.getParameterMappings();if (parameterMappings ! null) {for (int i 0; i parameterMappings.size(); i) {ParameterMapping parameterMapping parameterMappings.get(i);if (parameterMapping.getMode() ! ParameterMode.OUT) {Object value;String propertyName parameterMapping.getProperty();if (boundSql.hasAdditionalParameter(propertyName)) { // issue #448 ask first for additional paramsvalue boundSql.getAdditionalParameter(propertyName);} else if (parameterObject null) {value null;} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {value parameterObject;} else {MetaObject metaObject configuration.newMetaObject(parameterObject);value metaObject.getValue(propertyName);}TypeHandler typeHandler parameterMapping.getTypeHandler();JdbcType jdbcType parameterMapping.getJdbcType();if (value null jdbcType null) {jdbcType configuration.getJdbcTypeForNull();}try {typeHandler.setParameter(ps, i 1, value, jdbcType);} catch (TypeException | SQLException e) {throw new TypeException(Could not set parameters for mapping: parameterMapping . Cause: e, e);}}}}}重点关注 TypeHandler typeHandler parameterMapping.getTypeHandler();JdbcType jdbcType parameterMapping.getJdbcType();if (value null jdbcType null) {jdbcType configuration.getJdbcTypeForNull();}try {typeHandler.setParameter(ps, i 1, value, jdbcType);} catch (TypeException | SQLException e) {throw new TypeException(Could not set parameters for mapping: parameterMapping . Cause: e, e);}根据参数映射拿到类型处理器就是策略模式的应用不同的类型处理器setParameter方法实现并不一样这就是不同的参数类型使用不同的类型处理器处理。 在解析结果集时也是一样的不同的类型需要使用不同的类型处理器获取结果 DefaultResultSetHandler#getPropertyMappingValue通过ResultMap的属性映射 private Object getPropertyMappingValue(ResultSet rs, MetaObject metaResultObject, ResultMapping propertyMapping, ResultLoaderMap lazyLoader, String columnPrefix)throws SQLException {if (propertyMapping.getNestedQueryId() ! null) {return getNestedQueryMappingValue(rs, metaResultObject, propertyMapping, lazyLoader, columnPrefix);} else if (propertyMapping.getResultSet() ! null) {addPendingChildRelation(rs, metaResultObject, propertyMapping); // TODO is that OK?return DEFERRED;} else {final TypeHandler? typeHandler propertyMapping.getTypeHandler();final String column prependPrefix(propertyMapping.getColumn(), columnPrefix);return typeHandler.getResult(rs, column);}}DefaultResultSetHandler#applyAutomaticMappings自动映射也是一样的 private boolean applyAutomaticMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, String columnPrefix) throws SQLException {ListUnMappedColumnAutoMapping autoMapping createAutomaticMappings(rsw, resultMap, metaObject, columnPrefix);boolean foundValues false;if (!autoMapping.isEmpty()) {for (UnMappedColumnAutoMapping mapping : autoMapping) {final Object value mapping.typeHandler.getResult(rsw.getResultSet(), mapping.column);if (value ! null) {foundValues true;}if (value ! null || (configuration.isCallSettersOnNulls() !mapping.primitive)) {// gcode issue #377, call setter on nulls (value is not found)metaObject.setValue(mapping.property, value);}}}return foundValues;}